1. Field of the Invention
The present invention relates to wellbore completion. More particularly, the invention relates to a system of completing a wellbore through the expansion and joining of tubulars. More particularly still, the invention relates to the expansion of one tubular into another tubular so as to create a downhole seal therebetween.
2. Description of the Related Art
Hydrocarbon and other wells are completed by forming a borehole in the earth and then lining the borehole with steel pipe or casing to form a wellbore. After a section of wellbore is formed by drilling, a section of casing is lowered into the wellbore and temporarily hung therein from the surface of the well. Using apparatus well known in the art, the casing is cemented into the wellbore by circulating cement into the annular area defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the wellbore for production of hydrocarbons. Cementing also protects the surrounding formation environment.
It is common to employ more than one string of casing in a wellbore. In this respect, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The well is then drilled to a second designated depth, and a second string of casing, or liner, is run into the well. The second string is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The second liner string is then hung in the wellbore, usually by some mechanical slip mechanism, and cemented. This process is typically repeated with additional casing strings until the well has been drilled to total depth. In this manner, wells are typically formed with strings of casing of an ever-decreasing diameter.
In some instances, wells are completed by perforating the lowest string of casing to provide a fluid path for hydrocarbons to enter the wellbore. From there, hydrocarbons flow into a screened portion of another smaller tubular, referred to as the production tubing. The production tubing is isolated with packers to seal off the annular area between the production tubing and the casing, thereby urging hydrocarbons into the production tubing.
In other completions, the lowest string of casing is preslotted before being run into the wellbore. A packer having a polished bore receptacle is positioned in the liner above the perforated region. A polished bore receptacle has a smooth cylindrical inner bore designed to receive and seal a tubular having a seal assembly on the outer surface of its lower end. The lower end of the production tubing is inserted into the polished bore receptacle. In this regard, the production tubing is lowered into the wellbore and xe2x80x9cstungxe2x80x9d into the polished bore receptacle of the packer to form a sealed connection. Fluid communication is thereby achieved between the producing zones of the well and the surface.
The body of a packer necessarily requires wellbore space and reduces the bore size available for production tubing and downhole production equipment. Therefore, there is a need for a packer for sealing a downhole annular area which is expandable, thereby providing a larger bore space to accommodate production tubing and equipment.
Emerging technology permits wellbore tubulars to be expanded in situ. An application of this is disclosed in U.S. Pat. No. 5,348,095, issued to Worrall, et al., in 1994. Worrall, et al., teaches the use of a conical tool downhole in order to expand a portion of a tubular into a surrounding formation wall, thereby sealing off the annular region therebetween.
It is known by inventor to utilize an expander tool having hydraulically activated rollers in order to expand an inner tubular into fluid communication with a larger outer tubular. The expander tool is lowered into the inner tubular on a working string, and positioned at the desired depth of expansion. Rollers disposed radially around the body of the expander tool are then actuated so as to apply an outward radial force from within the inner tubular. The body of the expander tool is then rotated so as to expand the inner tubular circumferentially into the outer tubular.
A shortcoming with the use of rotating expander tools is the likelihood of obtaining an uneven expansion of a tubular. In this respect, the inner diameter of the tubular that is expanded tends to assume the shape of the compliant rollers of the expander tool, including imperfections in the rollers. Also, the inside surface of the tubular is necessarily roughened by the movement of the rollers of the expander tool during expansion. Moreover, the compliant rollers are of a limited length, meaning that the working string must be moved up and down in order to apply the actuated rollers to different depths of a tubular to be expanded. This creates the likelihood that some portions of a tubular may be missed in the expansion process. The overall result is that the inner diameter of the expanded tubular is not perfectly round and no longer has a uniform inner circumference.
However, because of the above disadvantages with the roller-type expander tool, it is difficult to create a seal between an outer tubular and an inner expanded tubular dowhole. This, in turn, renders it impractical to utilize the roller-type expander tool for expanding the top of a liner to receive production tubing without a separate packer having a polished bore receptacle.
There is a need, therefore, for a method of creating a downhole seal between utilizing expansion technology. There is also a need to apply expandable tubular technology to the placement of a string of production tubing into a lower string of casing. Still further, there is a need for a method that can create a polished bore receptacle in a tubular for sealingly engaging production tubing in a wellbore.
The present invention provides a method for creating a polished bore receptacle, ii situ, using a standard tubular. The method is accomplished through tubular expansion technology.
The method of the present invention first comprises positioning a lower string of casing into a wellbore. The top portion of the lower string of casing will necessarily overlap with the bottom end of an intermediate or upper string of casing. Then, a conical expander tool is lowered into the wellbore on a working string. The cone is configured to enter the top end of the lower string of casing, and then expand its inner diameter upon complete entry. The swaged cone is forced a selected distance into the lower string of casing so as to apply a radial force to the inner surface of the tubular, thereby radially expanding the top end of the lower string of casing.
The use of a conformed, conical expander tool provides a smooth expansion and gives a consistent radial dimension to the inner surface of the lower string of casing. The conical expander avoids the inconsistent expansion provided in connection with the roller-type expander tool.
Once the expander tool has been forced a selected distance into the lower string of casing, the expander tool is removed. A uniform polished bore receptacle is thus created. The lower end of the production tubing can then be sealably mated into the polished bore receptacle.